A catalyst is a substance that increases the rate of a chemical reaction without, itself, being consumed in the reaction. Catalysts function by lowering the activation energy associated with the rate-determining step in a chemical reaction. As a result, the chemical reaction is accelerated.
Catalysts may be used in numerous applications. For example, electrochemical devices (e.g., fuel cells, batteries) may utilize catalysts. These devices can include electrodes (i.e., an anode and a cathode) with a solid or liquid ionic conducting and electronically insulating phase therebetween. Fuel materials are brought in contact with the anode and an oxidizing gas (e.g., oxygen) is brought in contact with the cathode. The fuel material may be oxidized in a chemical reaction which may be accelerated by the presence of the catalyst at the anode. The oxidizing gas is reduced in a chemical reaction which also may be accelerated by a catalyst at the cathode. The device generates electricity when electrons generated in the fuel oxidation reaction at the anode flow through an external circuit to the cathode where the electrons are consumed in the reduction reaction.
A number of different materials may be suitable catalysts for reactions that occur at electrodes in electrochemical devices. Examples of suitable catalysts include metals such as platinum and palladium, as well as alloys and compounds thereof. Because such catalytic materials are relatively expensive, it would generally be desirable to use less catalytic material if sufficient catalytic activity can be maintained.